Well Testing Essay

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Schlumberger

Basic Petroleum Engineering

FTC

Well Testing
Well Testing
Flow Regimes
Basic Equation
Well Testing
Drawdown Test
Build up Test
IPR Test
Summary

Notes

© JJ Consulting 1997

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Schlumberger

Basic Petroleum Engineering

FTC

Well Testing Theory

The pressure wave is likened to a wave in a pool after a stone has been dropped into it. At the earliest time the wellbore and zones close to it are influencing the response, at later time it is the reservoir boundaries.
The idea is very simple but gives a lot of information about the reservoir in spite of the simple measurement of pressure and time.

A well test is conducted by making a sudden change in flowrate and then measuring the changes in the pressure with respect to time.
The pressure wave travels out into the reservoir
“seeing” deeper as time goes on.

rate Q

Producing

Shut in

Notes

0

Time, t

Bottom hole
Pressure P

0

Time, t
0

2
2
2

Schlumberger

FTC

Basic Petroleum Engineering

Flow In the well

Slug and Plug flow are not very efficient as they lose energy as they tumble. FLOW REGIMES

LIQUID VELOCITY

102

10

The flow in the wellbore/casing/tubing of oil will take a number of forms.
The flow starts as single phase, as gas comes out of solution the flow regime changes first to bubble flow, small gas bubbles in the oil. The other states may or may not happen in the tubing depending on the pressures and gas oil ratio.

REGION I

REGION III

TR

AN

SIT

IO

N

REGION II

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BUBBLE FLOW

Notes

10-1

PLUG FLOW
1

MIST FLOW

SLUG FLOW
10

102

103

GAS VELOCITY

The actual flow regime depends on a number of factors, such as gas-oil-ratio and pressures.

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Schlumberger

Basic Petroleum Engineering

FTC

The idea of radial flow seems obvious as the fluid is coming from all directions in the reservoir.

Flow in the formation
Flow form a reservoir into a borehole is normally radial

Well bore

Notes

It flows from the surrounding reservoir into the borehole, equally on all sides
This model is used to compute flow rates and pressure distributions

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Schlumberger

Basic Petroleum Engineering

FTC

Types of flow

fracture will cause the flow to be linear, not radial. An induced or
Other forms of flow are possible near the wellbore.However as thenatural pressure/flow moves further out into the reservoir the flow is moving radially to reach the fracture.

Radial Flow

Notes
Linear Flow

Bi-Linear Flow
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Schlumberger

Basic Petroleum Engineering

Assuming radial flow and knowing some parameters, Pwf, Pi, rw, h, re. the pressure at any point in the reservoir, P, can be described in terms of known or measured quantities.

FTC

Radial Flow Model

h

PWF

P

Pi i rw r Notes re This is the model for flow in the ideal case
Constant pressure at the boundary, Pi
Reservoir thickness, h
Reservoir radius re
Wellbore radius is rw
Pwf, is the flowing pressure
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Schlumberger

Basic Petroleum Engineering

FTC

Flow States

The pressure time graph is roughly split into three regions. The final region is when the reservoir reaches its steady state. As this is unknown, it could have arrived at the reservoir limits, or a fault or the pressure disturbance created by a nearby well, this region cannot be easily described. The transition is equally ill defined. However in the transient period radial flow can be assumed and hence the problem analysed.

Transient period Transition

Pressure

Pseudo-Steady
State

Notes
Time

The transient period is also known as infinite acting radial flow
All tests have some time in this region hence this is the zone normally analysed.
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Schlumberger

Basic Petroleum Engineering

FTC

Basic Equation

Note the units used determine the constant.
The
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